How to disable disappearing of Stencil Brush while navigating viewport in Texture Paint Mode?
Instead of using only the Stencil Brush, you can use the old method of multiple UV layered images projected from different views and then use the Clone tool in the 3d viewport to paint from the source layers in the final texture layer. After you get the bulk of your paint finished, you can then use the Stencil Brush to fix areas that need cleanup.